In the field of horizontally disposed metal or plastic siding panels for building exteriors, a variety of mounting means have been utilized to secure the panels to the underlying wall structure. In some cases, the panels themselves have been directly nailed or stapled to the underlying structure. In other cases, the panels have been interlocked and suspended from short clips or long nailing strips which are in turn nailed or otherwise secured to the underlying building structure. Representative showings of these interlocking and securing arrangements are found in U.S. Pat. Nos. 2,820,535, 3,214,876, 3,520,099, 3,552,078 and 3,703,795.
The prior art recognized the need to permit relative longitudinal movement between the suspended siding panel and any nailing clip or strip from which it was suspended. This requirement results from differential thermal expansion and contraction between the siding panel and the nailing clip or strip. Differing expansion and contraction of these materials is caused by several factors. First, the panels may be directly exposed to substantial temperature fluctuations and direct solar heating, while the nailing clips or strips are located behind such panels and therefore are not exposed to direct solar heating. Secondly, the panels and nailing clips or strips may be formed of different materials. For example, the nailing clips or strips are generally fabricated of aluminum or steel, while the siding panels may be fabricated of vinyl, aluminum, steel or other plastic or metal materials. The necessary relative movement has generally been provided by interlocking horizontally extending tracks or channels which permit the panel to hang from the nailing strip or clip, while permitting longitudinal sliding of the panel.
However, the thermal expansion and contraction phenomenon also creates a problem in terms of the extent of horizontal overlap between the longitudinal ends of adjacent panels. If the extent of overlap is initially too small, then subsequent contraction of both panels during colder weather may eliminate the overlap, creating an unsightly exposure of the underlying structure. Conversely, if the overlap is initially too great, subsequent thermal expansion may cause the underlying nailing strips or siding panels to establish an interfering abutting relationship, causing bulging or buckling of these components. The abutment of overlapped panels occurs, not at the visible longitudinal ends of the panels, but more typically at the interlocking flange formations. That is, the formations at the upper or lower longitudinal edges of each panel, where the panels interlock with upwardly or downwardly adjacent panels or nailing strips or clips, generally do not run the full longitudinal lengths of the siding panel. They terminate before the extreme longitudinal end of the panel to permit horizontally adjacent panels to overlap each other without interference by these formations. Therefore, horizontally adjacent panels which are installed in overlapping relationship at their longitudinal ends are free to lengthen without interference with each other, but only until those interlocking formations abut each other.
Another problem or inconvenience that arises with the use of elongated nailing strips is that the strips are not sufficiently stiff to survive rough handling during packing, unpacking or assembly. If they are bent, a resulting permanent crease or kink can restrict the cross-sectional openings that exist between the flange or channel formations that are designed to interlock with those on the siding panels. The result of such kinking is interference with the assembly of a panel-nailing strip pair. This problem is aggravated by the fact that a typical panel may be twelve feet long, and therefore the handling of these long, readily-bendable nailing strips as they are unpacked from a box and slidably assembled along the length of a siding panel creates a high risk of damage.
Accordingly, it would be desirable to provide a means for permitting factory pre-assembly of each nailing strip-siding panel pair, and in a manner that, while permitting subsequent relative slidable movement to accommodate thermal expansion contraction, prevents the panel from becoming disassembled from the nailing strip during handling prior to installation.